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Post by sts60 on May 3, 2006 9:07:16 GMT -4
Depends on what you mean by "lethal". Seriously. Sections of the Van Allen belt would deliver a lethal dose if you stayed there long enough. Ordinary levels of cosmic rays and whatnot would likely cause cancer, eventually, if you lived there long enough. Of course, Shuttle/Mir/ISS astronauts, who regularly traverse part of the Van Allen belts, do just fine, so there's no sudden lethality. Thanks for the bump, turbonium. Take the time you need to marshal your arguments so we can tear you limb from limb discuss them in a calm and reasoned manner.
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Post by JayUtah on May 3, 2006 13:22:27 GMT -4
Biological dosimetry is not an either-or proposition. Even elevated levels of background radiation have biological effects over a human life span. I live in Salt Lake City, Utah, at an elevation of well over 1,000 meters. My level of background radiation exposure is higher than that of someone who lives in Houston. And so I am at a greater risk for cancer and other health issues.
At the other end of the spectrum is blasts of thousands of REM which you can get from nuclear weapons, or from the very uncommon solar events if you were unprotected. Those will kill you in minutes or hours simply by ionizing enough of your body to make its chemical reactions stop working and by causing enough immediate damage to overwhelm your recuperative capacity.
Somewhere in between you have space exploration.
Obviously I don't want to be an astronaut if it's going to shorten my life by 30 years. So I'm hesitant to sign up for long-term missions if that's what it's going to take. But for the short missions the risk of dangerous exposure was just rather low. And you have to understand the variables involved and how they affect each other numerically in order to understand how best to solve radiation problems.
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Post by sts60 on May 3, 2006 13:52:25 GMT -4
My level of background radiation exposure is higher than that of someone who lives in Houston. And so I am at a greater risk for cancer and other health issues.
Except that you are neglecting the automotive smog and, ah, contributions from the many refineries along the Ship Channel and points east. So I'd say you're probably at less risk.
Obviously I don't want to be an astronaut if it's going to shorten my life by 30 years. So I'm hesitant to sign up for long-term missions if that's what it's going to take.
Hmmm... I certainly wouldn't mind signing up for a five-year mission when I'm 90, even if would shorten my life by 30 years. Maybe John Glenn has just achieved the minimum age for long-term space missions, and Story Musgrave just has to wait, the pup!
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reynoldbot
Jupiter
A paper-white mask of evil.
Posts: 790
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Post by reynoldbot on May 3, 2006 16:08:00 GMT -4
Traveling on Houston highways has taken a good five years off my life through stress and probably increased my chance of having an aneurysm three-fold.
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Post by echnaton on May 3, 2006 16:20:22 GMT -4
Traveling on Houston highways has taken a good five years off my life through stress and probably increased my chance of having an aneurysm three-fold. You just need to follow the Texas model for relaxed driving. Leave the stress behind and go so fast it can’t catch up with you. I guess you weren’t on the Continental Airlines jet yesterday? Talk about a few hours of stress. A regional airliner bound to Minneapolis blew both tires on the left landing gear on takeoff and had to take a scenic tour of Harris and surrounding counties for nearly three hours to burn off fuel before making a landing. The pilots landed it safely and everyone was OK.
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Post by sts60 on May 3, 2006 16:46:09 GMT -4
Here's stress related to the last two posts: Go to Hobby(edit - I meant Ellington) with two colleagues to catch puddle-jumper to Intergalactic for trip to Orlando. Plane broken. Cram into one car (the guy wedged in back has a signature gracing some of the Apollo TV camera technical documents, BTW), race up to IAH, park, sprint to gate 5 minutes before scheduled departure. Plane is sitting there with jetway closed. Continental gate agent says, "The plane's left" and cannot be persuaded to acknowledge presence of plane about 20 feet away.
I don't recall much else, but we didn't kill the cretin for some reason, and got first-class tickets on a later flight. That was when Continental was at their customer-service nadir.
OK, now about translunar radiation environments...
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reynoldbot
Jupiter
A paper-white mask of evil.
Posts: 790
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Post by reynoldbot on May 3, 2006 23:04:54 GMT -4
Man echnaton that's kind of creepy. I lived in Harris county for 10 years and still do over the summer, and I currently live in Minneapolis for school. I'm glad I don't generally fly to either place.
I hate going to Hobby airport. It's way out in the middle of some neighborhood and is impossible to get to or out of quickly. IAH is much more accessible. Anytime I fly to or from Houston I make sure it's through IAH.
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Post by Ranb on May 4, 2006 0:27:10 GMT -4
I work in the nuclear field as a radiological control tech, so I do understand basics about radiation exposure. A few basic searches on the net showed little about how radiation levels were measured other than on a few of the early space shots. I guess I just need to search more.
I was curious as to whether or not anyone had measured levels high enough to make dying of radiation exposure in space (such as 3 rem per hour continuous) in as little as two weeks a real possibility. According to my training, as little as 0.1 mr/hr continuous exposure for a year will result in a small but hardly significant increase in the risk of cancer. I am willing to be exposed to more if I was able to grab a seat on a trip to Mars.
Ranb
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Post by JayUtah on May 4, 2006 10:10:37 GMT -4
Those continuous levels occur only within the deepest, darkest reaches of the Van Allen belts. However, a particularly noxious X-class solar event can dump hundreds of rem at you in a space of 18 hours or so.
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Post by turbonium on May 6, 2006 7:42:41 GMT -4
I'd like to begin with Van Allen's published documentation on the VA Belts. The following is basic knowledge to most here but I'd like to make note of it for the discussion anyway. The 1957 and 1959 NAS documents linked below mention that the Geiger-Mueller Counter used lead (and iron) shielding during the Explorer IV project, when the earlier, unprotected G-M Counters malfunctioned. The shielded counters confirmed that the malfunction was due to extremely high radiation levels. www.pubmedcentral.gov/pagerender.fcgi?artid=528387&pageindex=1#pagewww.pubmedcentral.gov/pagerender.fcgi?artid=222697&pageindex=1#pageResearch conducted in 1960 resulted in the following... June 21
Robert O. Piland, Head of the STG Advanced Vehicle Team, and Stanley C. White of STG attended a meeting in Washington, D. C., sponsored by the NASA Office of Life Sciences Programs, to discuss radiation and its effect on manned space flight. Three consultants presented their views: John R. Winckler of the University of Minnesota, a cosmic-ray physicist; Cornelius A. Tobias of the University of California, a radiologist specializing in radiation effects on cells and other human subsystems; and Col. John E. Pickering, Director of Research at the Air Force School of Aviation Medicine. Their research showed that it would be impracticable to shield against the inner Van Allen belt radiation but possible to shield against the outer belt with a moderate amount of protection.(emphasis added) history.nasa.gov/SP-4009/v1p1.htmThe research done by Van Allen and others in the late 1950's and onward led to the realization that any manned spacecraft going through the belts would require significant shielding to protect astronauts from harmful radiation. The further problem was whether or not it was even possible. As the research noted above stated, protection against the inner belt was "impractical" for manned space flight. I would like to know what research, if any, was ever done subsequently that invalidated the original findings that concluded substantial shielding was necessary to prevent radiation from harming or perhaps killing humans within the belts? Why were there no animals used in test flights except within low Earth orbit? The hazardous effects to living organisms from the various types of radiation within the belts, in deep space, and on the Moon were unknown and never tested. Even now, current projects are aiming to study what the effects of radiation are in space and on the Moon to organic material.... To carefully measure and map the Moon's radiation environment, NASA is developing a robotic probe to orbit the Moon beginning in 2008. Called the Lunar Reconnaissance Orbiter (LRO), this scout will pave the way for future human missions not only by measuring space radiation, but also by hunting for frozen water and mapping the Moon's surface in unprecedented detail.Didn't 7 Apollo missions measure space radiation going to the Moon and back? And why are future manned missions to the Moon, even preliminary "short stay" missions, going to be preceded by probes that measure levels for the various types of radiation that we need to know if they are hazardous to future manned visits? Since short stay visits were no problem 35 years ago, why can't they at least just pick up where they left off? When galactic cosmic rays collide with particles in the lunar surface, they trigger little nuclear reactions that release yet more radiation in the form of neutrons. The lunar surface itself is radioactive!
So which is worse for astronauts: cosmic rays from above or neutrons from below? Igor Mitrofanov, a scientist at the Institute for Space Research and the Russian Federal Space Agency, Moscow, offers a grim answer: "Both are worse."Why didn't the dosimeters worn by the astronauts measure neutron radiation emanating from the lunar surface? Were they even capable of measuring it? The probe measured it in orbit, while the astronauts didn't know it existed even though they were standing on the surface itself? www.physorg.com/news6342.html I'm leaving this first post sort of "open ended" with general questions to get the thread going for now....so you can start "tearing me limb from limb!"
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Post by turbonium on May 6, 2006 8:07:31 GMT -4
Another point while I think of it. Sibrel interviewed Alan Bean, asking him about the VA belts. Bean said he didn't think they went high enough to have gone through them!?!
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Post by jones on May 6, 2006 11:22:23 GMT -4
I'd like to see a source or maybe a transcript of that interview...
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Post by Jason Thompson on May 6, 2006 11:31:05 GMT -4
The research done by Van Allen and others in the late 1950's and onward led to the realization that any manned spacecraft going through the belts would require significant shielding to protect astronauts from harmful radiation. The further problem was whether or not it was even possible. As the research noted above stated, protection against the inner belt was "impractical" for manned space flight.
Define ‘substantial shielding’. Different types of radiation require different types of shielding. Six feet of lead is substantial shielding. So is a few millimetres of plastic and aluminium. It all depends on the type of radiation.
Define what kind of manned space flight they were referring to when they described the impracticability of shielding. There is a significant difference from a flight that spends a long time orbiting within the belts and one that passes through them. Radiation effects are cumulative, and the human body is very good at recovering. Sit in radiation at low levels for too long and you’ll get sick or die. Experience a short, strong burst and you’ll recover quickly with few ill effects once you leave the region of radiation.
I would like to know what research, if any, was ever done subsequently that invalidated the original findings that concluded substantial shielding was necessary to prevent radiation from harming or perhaps killing humans within the belts?
Information on the radiation in space was returned by many probes between the initial discovery of the belts and the manned flight to the Moon. The more data is available, the more the conclusions are modified, until it may be the case that original conclusions turn out to be erroneous. This is neither suspicious nor uncommon in science.
Why were there no animals used in test flights except within low Earth orbit? The hazardous effects to living organisms from the various types of radiation within the belts, in deep space, and on the Moon were unknown and never tested.
You don’t necessarily need to send living organisms into a radioactive environment to assess it. If the type of radiation is known, the flux is known and the type of shielding available is known you can assess whether it is safe for humans without actually sending anything alive out there. Plenty of unmanned probes returned data about the environment within and above the van Allen belts. Additionally, Zond 5 sent biological samples around the Moon. They suffered no ill effects from radiation.
Didn't 7 Apollo missions measure space radiation going to the Moon and back?
Yes.
And why are future manned missions to the Moon, even preliminary "short stay" missions, going to be preceded by probes that measure levels for the various types of radiation that we need to know if they are hazardous to future manned visits? Since short stay visits were no problem 35 years ago, why can't they at least just pick up where they left off?
They can, but why waste a few short stay manned missions to assess the environment when a few cheaper unmanned satellites will provide the preliminary data you need to start the new phase of lunar exploration with something considerably better than an Apollo-style mission? Wouldn’t you want the best, most up-to-date information gathered with the most up-to-date equipment if you had the chance?
Why didn't the dosimeters worn by the astronauts measure neutron radiation emanating from the lunar surface? Were they even capable of measuring it? The probe measured it in orbit, while the astronauts didn't know it existed even though they were standing on the surface itself?
What is the flux of radiation from the lunar surface?
The basic points that must be clearly understood before any meaningful discussion about radiation can take place are:
The ability to detect radiation does not mean the environment is short-term deadly. We are all currently bathed in low-level radiation from natural radioactive elements in the Earth.
Short high doses are less of a problem than long low doses.
Different types of radiation require different types of shielding.
The current plan for lunar exploration is for long stays and possibly a permanent human presence. This requires a much more detailed knowledge of the radiation environment than the short duration missions of the Apollo era. Apollo basically asked: ‘does the data indicate serious health issues for two weeks in space?’ Now we need to know ‘what are the potential health issues for a crew spending months or years on the Moon’. They are two very different questions.
As to Al Bean's comment, I'd like a source or transcript. Bean would not have made such an elementary error. Sibrel, on the other hand, may well have either a) misinterpreted a statement by Bean regarding the Apollo trajectories being designed to bypass the worst areas of the belts, or b) have intentionally misunderstood, twisted the words or made the whole thing up. That may sound harsh, but personal experience with Sibrel leads me to the conclusion that he is not above lying to try to bolster his arguments.
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Post by jones on May 6, 2006 11:34:06 GMT -4
From wikipedia: (regarding radation exposure in the van allen belts)
An object satellite shielded by 3 mm of aluminum will receive about 2500 rem (25 Sv) per year. _______________________________
How much time was spent on average in the van allen belts throughout the apollo missions? I've heard around 4 hours?
So every hour in the van allen belts, you'll take about .285 rem from the van allen belts. Is that a lethal dose? From what I understand a lethal dose of radiation is about 450 rem?
I'm sure if I'm wrong one of the experts here will correct me.
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Post by sts60 on May 6, 2006 20:42:42 GMT -4
Thanks for the post, turbonium. Be patient in return while I work on specific stuff.
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